In a known manner, a brush-holder is fitted on the shaft of the rotor of a starter such as to make the brushes cooperate with an electrical collector which is integral with the rotor shaft. The brush-holder comprises a support plate which supports a set of cages, each of which is used to accommodate a brush. The brushes, which are made of electrically conductive material, permit the electrical supply to the rotor by switching of the electric current in the conductors of the rotor.
For this purpose, each brush comprises a face designed to rub against the conductive strips of the collector which are connected to the rotor winding. A resilient means, such as a spring, exerts on each brush received in a cage a force in the direction of the collector, in order to ensure the contact between the brush and the strips of the collector.
The brushes have alternating polarities. Thus, the brushes with positive polarity are connected electrically, via their respective braid, to an inter-brush connector to which there is also connected electrically the supply wire obtained from the contactor of the starter. In addition, the brushes which are designed for the current return are connected electrically to the earth of the machine by means of their respective braid welded on the plate.
In certain brush-holder configurations, it is known to use a spring of the spiral type comprising a wound part which is fitted on a lug, as well as an arm which extends from an end of the wound part, and is designed to be supported on an end face of the brush opposite the face in contact with the strips of the collector. In order to allow the spring to apply a thrust to the brush, the arm passes by means of an opening provided in a lateral wall of the brush cage.
The problem is to be able to produce springs with a relatively great thrust force, in the knowledge that the diameter of the wound part is limited because of the need to obtain a compact assembly, and that the thickness is also limited in order to be able to use standard springs at a reduced cost. The invention thus proposes to modify the width parameter of the spring in order to adapt its force, without modifying the structure of the brush case, since an increase in the opening to permit the passage of the arm of the spring would make the cage mechanically fragile.